The number of devices, and also the number of different types of devices, that are capable of communicating via radio interfaces with radio access networks is enormous, not least due to the rapid development of mobile telephone networks and wireless computer networks. Needless to say, such radio communication capable devices now include consumer electronic apparatuses of many kinds as well as devices in more industrial fields involving, for example, machine-to-machine communication.
A feature that is common to many of these types of devices is that they are powered by a very limited energy source such as a battery. An inherent problem to such devices is that of how to match the ever increasing demand for data processing capability with a limited capability of storing energy in the battery. One group of solutions to this problem involves the concept of operational states. That is, depending on the requirements of the device to provide processing capability it is possible to control the device to operate in two or more states that differ in terms of how much power is needed. For example, a device having a display screen may not need to actively display content during periods when no one is looking at the display screen. Another example is where it can be determined that processing circuitry or radio communication circuitry is not needed for specific time intervals, and therefore the device can be set to operate in a state where such circuitry is less active than in a normal state of activity.
This concept of operational states has been incorporated in radio access technologies such as the third generation partnership project, 3GPP, radio communication standards. Examples of these are the cellular wideband code division multiple access, WCDMA, and the long term evolution, LTE, technologies. Other systems such as the institute of Electrical and Electronics Engineers', IEEE, 802.11 standards also include a power save mode.
In 3GPP systems operating according to WCDMA and LTE the different states are called radio resource control, RRC, states and include an idle state and connected states. In WCDMA there are five RRC states; Cell_DCH, Cell_FACH, URA_PCH, Cell_PCH, and Idle. Data transfer between a device, which often is denoted by the term user equipment or simply UE, and the network is only possible in Cell_FACH and Cell_DCH states.
The Cell_DCH state is characterized by dedicated channels in both the uplink and the downlink. The UE location is known with an accuracy of cell level. This corresponds to continuous transmission and reception and this state has the highest battery consumption.
The Cell_FACH state does not use dedicated channels and hence less control channel overhead, thus allowing better battery consumption, but at the expense of a lower uplink and downlink throughput. The UE location is known with an accuracy of cell level.
URA_PCH and Cell_PCH are states in which the battery consumption is very low but still allow for reasonable fast transitions to the states in which data transfer can occur. The UE location is known with the accuracy of a so-called registration area, RA, or cell respectively, however paging is needed to reach the UE.
Idle have the lowest battery consumption but the transition from idle to a state in which data transfer can occur takes the longest time. The UE location is known with an accuracy of a so-called routing area.
FIG. 1a presents a state of the art RRC state transition scheme also referred to as channel switching scheme, as one is connect to different data channels in the states. The RRC state up-switches are typically based on radio link protocol, RLC, buffer fill level thresholds and the down-switches are typically based on inactivity timers.
In LTE systems, there are two RRC states: RRC_IDLE and RRC_CONNECTED, as shown in FIG. 1b, where the former corresponds to the idle state of WCDMA. The RRC_CONNCTED state corresponds to CELL_DCH of WCDMA and has three modes, continuous reception, short DRX and long DRX where DRX stands for discontinuous reception. Hence, RRC_IDLE has the lowest battery consumption and varying consumption in RRC_CONNECTED depending on the mode configuration.
User equipment that operates according to release 7 or earlier of the 3GPP standard specifications may send a signal connection release message to force itself to RRC Idle state. This is referred to as fast dormancy. Hence, the UE may have its own internal down-switch timer which is shorter than the network down-switch timers. This is done without the control of the network.
An improvement to this is done in 3GPP release 8. The release 8 fast dormancy solution allows the UE to signal to the network that the data transmission is completed. However, in the release 8 fast dormancy the network controls the down-switch of the UE and can decide to move the UE to another RRC state than idle for example URA_PCH or not to down-switch at all.
The triggering of fast dormancy from the UE may be based on different inputs. For example radio inactivity and screen status, i.e. whether a display screen is on or off. FIG. 2 gives an example of a fast dormancy triggering situation where the inactivity timer is set to 3 seconds, and also that the display screen needs to be off for at least 3 seconds. Both conditions need to be fulfilled to trigger fast dormancy.
There is always a trade of between the resource consumption, for example UE battery or processor load of a node in the network with which the UE communicates, of switching a UE from a connected state, e.g. CELL_DCH, CELL_FACH, to a standby state, e.g. CELL_PCH and URA_PCH, or staying in the connected state until next data burst is sent to or from the UE. Typically, a fast down-switch is beneficial for UE battery consumption while staying longer in the higher state is more beneficial for processor load in the network node.
The time between data bursts are referred to as the Idle Time Between bursts, or ITB. Hence, at a certain ITB length the cost (in consumed resources) is the same for staying on a given state or switching down and then up to the same state. This ITB is referred to as the threshold ITB.
With the increased number of UEs, particularly UEs in the form of so-called smart phones, operating in the radio networks the bottleneck has many times become the connection handling in the network nodes due to the heavy signaling the UEs have put to the network. The increased signaling is due to that the UEs want to be released from the network in order to save their battery by performing a fast dormancy, and the new applications made available to the mobile devices.
Even though the network has more control of which state to send the UE to with 3GPP release 8 supported fast dormancy, e.g. instead of the UE going to Idle the network may send the UE to URA_PCH, the fast dormancy signaling from many UEs are still expected to have a significant negative impact on the resource consumption, e.g. processor load in the network nodes, and downlink power and uplink interference.
The underlying problem is that fast dormancy requests from the UE are sent with the sole purpose of minimizing the UE battery consumption. The processor load in the network nodes is not taken into account by the UE, which may put a heavy burden on the network nodes, nor the resources in, e.g., radio base stations for performing the actual transmission of the signaling messages.
One type of prior art solution to this is described in co-pending U.S. patent application Ser. No. 13/322,982, where the network node load is taken into account. However, experience has shown that it is difficult to do accurate predictions of long ITBs (i.e. to detect when to down-switch) since the predictions are based only on information available in the network.